The map positions of chloroplast genes that are frequently transcribed during heterotrophic growth (dark) or phototrophic growth (light) will be determined. Two complementary methods will be used: "Blot hybridization" of cloned chloroplast DNA fragments to fractionated chloroplast RNA, and positive hybridization-translation of chloroplast RNA after binding to to specific cloned chloroplast DNA fragments. These results and the known positions of rRNA and tRNA genes will make it possible to sequence the tRNA genes and the initial and terminal segments of the repeated rRNA gene sets and of the other frequently transcribed genes. The sequencing studies constitute the major part of this proposal.